In providing electrical circuits to a facility, such as a home, one or more branch circuits are wired to distribute electrical power to load devices, such as light fixtures or outlet receptacles. Typically, the receptacle or fixture is hardwired directly to the branch circuit, with power to the device being turned on or off at the device itself. For example, a light fixture might include a pull cord for actuating a switch, while a small appliance might include a power switch.
With recent technological developments it is both possible and advantageous to provide automated control of load devices to provide, for example, remote or timed switching. One such system directs all communication functions into a master system controller. This gives a homeowner flexible communication and power control from anywhere in the home there is a control panel or switch, or even anywhere there is a telephone, such as the car or office. An intelligent outlet receptacle or fixture block allows individual appliances or fixtures to be separately and automatically controlled as necessary or desired. To do so, some means must be provided for controlling switching of power to the load device. To be practical, the switching must be done inexpensively and accurately. A latching relay has been found to be readily adaptable to such an application. A latching relay is latched when connected to a positive polarity voltage source and unlatched when connected to a negative polarity voltage source.
A relay of the remnant latching type is permanently magnetized so that upon actuation by a relatively high current pulse of positive polarity an included plunger is magnetically retained in an actuated position. When a reverse polarity power source is connected the magnetic field is reduced so that a spring force returns the plunger to an unlatched position. A short duration pulse must be used to avoid over-magnetization with opposite magnetic polarity.
Because only a short duration pulse is used for latching and unlatching, it is important to ensure that the relay actually does change state when commanded to do so. Desirably, a feedback circuit is used to sense state of the relay. A known such feedback circuit senses relay status directly by sensing AC voltage applied to a load. However, such a circuit is susceptible to a delayed response if a load has a relatively large reactive component which might sustain voltage too long after the associated relay opens. If this occurs, the latching relay control might continue trying to shut off the relay. Repetitive driving of the relay can damage the relay or other components due to overheating. Also, this might result in over-magnetization with opposite magnetic polarity.
The present invention is intended to overcome one or more of the problems discussed above in a novel and simple manner.